As illustrated in FIG. 13, a seal ring-equipped ball bearing 1 is used in a rotation support section of an automobile transmission that supports a rotating shaft inside a casing (not illustrated in the figure) so as to rotate freely (refer to JP2011080497 (A), JP2011080527 (A), JP2002115724 (A), JP2001140907 (A)). In the seal ring-equipped ball bearing 1, a contact-type seal ring is equipped in order to prevent damage to raceway surfaces of the bearing rings or to the rolling surfaces of the rolling bodies due to metal abrasion powder that is generated in the engagement section of the transmission gears or the like and that gets into the rolling contact areas of the ball bearing 1.
More specifically, the seal ring-equipped ball bearing 1 includes a ball bearing 3 and a pair of seal rings 4. The ball bearing 3 includes: an outer ring 6 that has a deep-groove outer-ring raceway 5 around the middle section in the axial direction of the inner-circumferential surface thereof, and that is fastened inside the casing so as not to rotate even during use; an inner ring 8 that has a deep-groove inner-ring raceway 7 around the middle section in the axial direction of the outer-circumferential surface thereof, and that is fastened around the outside of a rotating shaft 2 so as to rotate together with the rotating shaft 2 during use; plural balls 9 as rolling bodies that are provided between the outer-ring raceway 5 and the inner-ring raceway 7 so as to roll freely; and a retainer 10 that holds the balls 9 so as to roll freely.
The pair of seal rings 4 are located between the inner-circumferential surfaces on both end sections in the axial direction of the outer ring 6 and the outer-circumferential surfaces of both end sections in the axial direction of the inner ring 8, and cover the openings on both ends in the axial direction of the ring-shaped internal spaces where the balls 9 are located that exist between the inner-circumferential surface of the outer ring 6 and the outer-circumferential surface of the inner ring. These seal rings 4 are configured so that an elastic member 12 that has a circular annular shape as a whole and that is made of an elastomer such as rubber is reinforced by a circular annular-shaped metal insert 11 that is made of metal plate such as steel plate. The outer-circumferential edge section of each elastic member 12 protrudes outward in the radial direction (up-down direction in FIG. 13) a little more than the outer-circumferential edge of the metal insert 11, and the protruding portions are locked into locking grooves 13 that are formed around the inner-circumferential surfaces of both end sections in the axial direction of the outer ring 6. On the other hand, the inner-circumferential edge section of each elastic member 12 sufficiently protrudes inward in the radial direction more than the inner-circumferential edge of the metal insert 11, and this protruding portion forms a seal lip 14. The tip end sections of the seal lips 14 penetrate inside seal grooves 15 that are formed around the outer-circumferential surfaces on both end sections in the axial direction of the inner ring 8, and the side surfaces of the tip end sections of the seal lips 14 come in sliding contact with the side surfaces in the axial direction of the seal grooves 15 to form sliding contact areas between the seal lips 14 and the seal grooves 15.
In the construction illustrated in FIG. 13, a transmission gear 16 having a toothed section (for example, helical gear) around the outer-circumferential surface thereof and that is formed around the middle section in the axial direction of the rotating shaft 2 is supported by a radial needle bearing 17 so that relative rotation is possible. An annular shaped spacer 18 is provided between the seal ring-equipped ball bearing 1 and the transmission gear 16. The surface on one end in the axial direction (left-end surface in FIG. 13) of a cylindrical shaped boss 19 that functions as the outer ring of the radial needle bearing 17 and that is provided in a portion near the inner diameter of the transmission gear 16 comes in contact by way of the spacer 18 with a flat load-bearing surface 35 that is provided on the surface on one end in the axial direction (right-end surface in FIG. 13) of the inner ring 8 of the seal ring-equipped ball bearing 1. With this kind of construction, by using the seal ring-equipped ball bearing 1, a gear reaction force that acts on the transmission gear 16 is supported, and the transmission gear 16 can be positioned in the axial direction. The outer-diameter dimension of the spacer 18 is about the same as the outer-diameter dimension of the boss 19, and is larger than the outer-diameter dimension D35 of the load-bearing surface 35 of the inner ring 8.
In this conventional construction, concave-groove shaped seal grooves 15 that are open on the end surfaces in the axial direction are provided around the outer-circumferential surfaces on both end sections in the axial direction of the inner ring 8, so when compared with construction in which seal grooves are not provided, the outer-diameter dimension D35 of the load-bearing surface 35 of the inner ring 8 becomes small. When the surface on one end in the axial direction of the boss 19 comes in direct contact with the load-bearing surface 35, the contact surface pressure on the contact surface between the load-bearing surface 35 and the boss 19 becomes high due to the contact surface area being small, and there is a possibility that the amount of wear will become large, so this is prevented by providing a spacer 18. However, providing the spacer 18 brings about different problems such as an increase in the number of parts and assembly work, and makes it more difficult to make the device more compact and lightweight. As illustrated in FIG. 14, it is feasible to eliminate the spacer by increasing the outer-diameter dimension of the inner ring 8 while keeping the outer-diameter dimension of the load-bearing surface 35 large, however, as the outer-diameter dimension of the outer ring 6 increases, the size of the seal ring-equipped ball bearing 1 increases.
On the other hand, instead of construction in which the tip-end edges of the seal lips are brought into sliding contact in the axial direction with the side surfaces in the axial direction of the seal grooves (seal-groove construction), it is possible to eliminate the seal grooves and to use construction in which the tip-end edges of the seal lips are brought into sliding contact in the radial direction with the outer-circumferential surface of the end sections in the axial direction of the inner ring (shaft-seal construction). However, in groove-seal construction, the tip end sections of the seal lips penetrate inside the seal grooves, so the design space (design area) for the seal lips in order to prevent interference with the retainer is kept large, and thus it is possible to improve the freedom of design when designing the seal rings, however, in shaft-seal construction, the design space for the seal lips becomes small, and thus the freedom of design when designing the seal rings is reduced. Moreover, in groove-seal construction, even when there is relative displacement in the radial direction between the outer ring and the inner ring, the areas of sliding contact move in the radial direction and the displacement can be absorbed, so it is possible to prevent the surface pressure (tension force) at the areas of sliding contact from increasing, however, in shaft-seal construction, it is necessary to absorb this kind of displacement through elastic deformation of the seal lips, so it becomes easy for the surface pressure at the areas of sliding contact to increase. Therefore, in shaft-seal construction, with an intention to keep the rotational resistance (dynamic torque) of the seal ring-equipped ball bearing low, it is difficult to keep the surface pressure at the areas of sliding contact low while maintaining the necessary seal characteristics.